Experimental Evidence for Polybaric Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles

Melekhova, Elena; Blundy, Jonathan D.; Robertson, R. E. A.; Humphreys, Madeleine C. S.

doi:10.1093/petrology/egu074

Cited by 118 publications

(124 citation statements)

References 85 publications

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“…A two-stage polybaric differentiation could account for the observed plagioclase and olivine compositions, as suggested for the evolution of St. Vincent magmas (Melekhova et al 2015). In this case, the olivine-bearing samples have crystallised from differentiated basaltic andesite magmas, rather than as residual assemblages from deep crustal source regions, where the melts were generated (Melekhova et al 2015). Olivines from Martinique have relatively low Fo and Ni contents, providing evidence of crystallisation from a melt that has undergone prior olivine fractionation and is consistent with early differentiation in the deep crust.…”

Section: Mineral Chemistrymentioning

confidence: 68%

“…In addition, the coexisting compositions have not been reproduced by experimental studies performed on appropriate melt compositions (Sisson and Grove 1993a;Pichavant and Macdonald 2007). A two-stage polybaric differentiation could account for the observed plagioclase and olivine compositions, as suggested for the evolution of St. Vincent magmas (Melekhova et al 2015). In this case, the olivine-bearing samples have crystallised from differentiated basaltic andesite magmas, rather than as residual assemblages from deep crustal source regions, where the melts were generated (Melekhova et al 2015).…”

Section: Mineral Chemistrymentioning

confidence: 94%

“…Experiments by Pichavant et al (2002) and suggest gabbronorite crystallisation at 0.4 GPa, 950-1016 °C and water contents from 3.9-6.9 wt% H 2 O. Experiments by Melekhova et al (2015) were run at higher pressures (0.7-1 GPa) and lower water contents (0.6-2.3 wt%) and the composition of phases were not as close to natural samples as Pichavant et al (2002) (Online Resource 6).…”

Section: Intensive Variables and The Origin Of Plutonic Xenolithsmentioning

confidence: 99%

“…In hydrous conditions at greater pressures and depths, plagioclase is likely to be absent (Melekhova et al 2015). Plagioclase-free assemblages have been sampled on Grenada (Stamper et al 2014) and St. Vincent (Tollan et al 2012) to the south of the Lesser Antilles arc and plagioclase appears later in the crystallisation sequence in plutonic xenoliths from Grenada.…”

Section: Intensive Variables and The Origin Of Plutonic Xenolithsmentioning

confidence: 99%

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Plutonic xenoliths from Martinique, Lesser Antilles: evidence for open system processes and reactive melt flow in island arc crust

Cooper

Davidson

Blundy

2016

Contrib Mineral Petrol

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Section: Mineral Chemistrymentioning

confidence: 68%

Section: Mineral Chemistrymentioning

confidence: 94%

Section: Intensive Variables and The Origin Of Plutonic Xenolithsmentioning

confidence: 99%

Section: Intensive Variables and The Origin Of Plutonic Xenolithsmentioning

confidence: 99%

See 2 more Smart Citations

Plutonic xenoliths from Martinique, Lesser Antilles: evidence for open system processes and reactive melt flow in island arc crust

Cooper

Davidson

Blundy

2016

Contrib Mineral Petrol

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“…14) in what has been termed a transcrustal magmatic system (TCMS) by Cashman, et al (2017). Xenolith crystallisation pressures indicate that a vertically-extensive crystal mush (crystals + melt) enables polybaric differentiation to occur in a hot zone extending from near the Moho to the upper crust (Melekhova et al 2015). This hot zone also contains elevated H 2 O contents in trapped melts, lending support to the idea of a hydrous mush dominated by amphibole (Davidson et al 2007).…”

Section: Bequia Plumbing Systemmentioning

confidence: 91%

Magma evolution beneath Bequia, Lesser Antilles, deduced from petrology of lavas and plutonic xenoliths

Camejo-Harry

Melekhova

Blundy

et al. 2018

Contrib Mineral Petrol

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Vol.:(0123456789) 1 3Contributions to Mineralogy and Petrology (2018) AbstractExtrusive and intrusive igneous rocks represent different parts of a magmatic system and ultimately provide complementary information about the processes operating beneath volcanoes. To shed light on such processes, we have examined and quantified the textures and mineral compositions of plutonic and cumulate xenoliths and lavas from Bequia, Lesser Antilles arc. Both suites contain assemblages of iddingsitized olivine, plagioclase, clinopyroxene and spinel with rare orthopyroxene and ilmenite. Mineral zoning is widespread, but more protracted in lavas than xenoliths. Plagioclase cores and olivine have high anorthite (An ≤ 98) and low forsterite (Fo ≤ 84) compositions respectively, implying crystallisation from a hydrous mafic melt that was already fractionated. Xenolith textures range from adcumulate to orthocumulate with variable mineral crystallisation sequences. Textural criteria are used to organize the xenoliths into six groups. Amphibole, notably absent from lavas, is a common feature of xenoliths, together with minor biotite and apatite. Bulk compositions of xenoliths deviate from the liquid line of descent of lavas supporting a cumulate origin with varying degrees of reactive infiltration by evolved hydrous melts, preserved as melt inclusions in xenolith crystals. Volatile saturation pressures in melt inclusions indicate cumulate crystallization over a 162-571 MPa pressure range under conditions of high dissolved water contents (up to 7.8 wt% H 2 O), consistent with a variety of other thermobarometric estimates. Phase assemblages of xenoliths are consistent with published experimental data on volatile-saturated low-magnesium and high-alumina basalts and basaltic andesite from the Lesser Antilles at pressures of 200-1000 MPa, temperatures of 950-1050 °C and dissolved H 2 O contents of 4-7 wt%. Once extracted from mid-crustal mushes, residual melts ascend to higher levels and undergo H 2 O-saturated crystallization in shallow, preeruptive reservoirs to form phenocrysts and glomerocrysts. The absence of amphibole from lavas reflects instability at low pressures, whereas its abundance in xenoliths testifies to its importance in mid-crustal differentiation processes. A complex, vertically extensive (6 to at least 21 km depth) magmatic system is inferred beneath Bequia. Xenoliths represent fragments of the mush incorporated into ascending magmas. The widespread occurrence of evolved melts in the mush, but the absence of erupted evolved magmas, in contrast to islands in the northern Lesser Antilles, may reflect the relative immaturity of the Bequia magmatic system.

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Crustal‐scale degassing due to magma system destabilization and magma‐gas decoupling at Soufrière Hills Volcano, Montserrat

Christopher

Blundy

Cashman

et al. 2015

Geochem Geophys Geosyst

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125

107

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Activity since 1995 at Soufrière Hills Volcano (SHV), Montserrat has alternated between andesite lava extrusion and quiescence, which are well correlated with seismicity and ground deformation cycles. Large variations in SO 2 flux do not correlate with these alternations, but high and low HCl/SO 2 characterize lava dome extrusion and quiescent periods respectively. Since lava extrusion ceased (February 2010) steady SO 2 emissions have continued at an average rate of 374 tonnes/day (6 140 t/d), and incandescent fumaroles (temperatures up to 610 o C) on the dome have not changed position or cooled. Occasional short bursts (over several hours) of higher ( 10x) SO 2 flux have been accompanied by swarms of volcano-tectonic earthquakes. Strain data from these bursts indicate activation of the magma system to depths up to 10 km. SO 2 emissions since 1995 greatly exceed the amounts that could be derived from 1.1 km 3 of erupted andesite, and indicating extensive partitioning of sulfur into a vapour phase, as well as efficient decoupling and outgassing of sulfur-rich gases from the magma. These observations are consistent with a vertically extensive, crustal magmatic mush beneath SHV. Three states of the magmatic system are postulated to control degassing. During dormant periods (10 3 to 10 4 years) magmatic vapour and melts separate as layers from the mush and decouple from each other. In periods of unrest (years) without eruption, melt and fluid layers become unstable, ascend and can amalgamate. Major destabilization of the mush system leads to eruption, characterized by magma mixing and release of volatiles with different ages, compositions and sources.

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Experimental Evidence for Polybaric Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles

Cited by 118 publications

References 85 publications

Plutonic xenoliths from Martinique, Lesser Antilles: evidence for open system processes and reactive melt flow in island arc crust

Plutonic xenoliths from Martinique, Lesser Antilles: evidence for open system processes and reactive melt flow in island arc crust

Magma evolution beneath Bequia, Lesser Antilles, deduced from petrology of lavas and plutonic xenoliths

Crustal‐scale degassing due to magma system destabilization and magma‐gas decoupling at Soufrière Hills Volcano, Montserrat

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